Color television apparatus



Jan. 23, 1962 H. T. STANLEY 1 COLOR TELEVISION APPARATUS Filed March 5, 1959 A l4 l3 l2 Flg. l.

Receiver B+ Load From B+ Supply 2o 7 ""Y I I I "'(I I I I8? l93 r' Fig. 2

\ wmuzssss INVENTOR Hurry T. Stanley. BY 5 6 3,018,401 COLOR TELEVISION APPARATUS Harry T. Stanley, Red Bank, N.J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Mar. 5, 1959, Ser. No. 797,435 4 Claims. (Cl. 313-85) This invention relates to color television receivers, and relates more particularly to the arrangement of field neutralizing coils for the picture tube or color television receivers.

Field neutralizing coils are commonly used with color picture tubes of the aperture mask type for correcting for the effect on their electron beams of axially aligned components of the earths magnetic field. Such a coil usually consists of several turns of wire wound in a ring having an internal diameter substantially equal to that of the face plate of the color picture tube with which it is to be used, and is usually mounted flush with the face plate. Such a coil is usually connected in parallel with a field neutralizing control consisting of a variable resistor and a double-pole, double-throw switch connected in parallel, this combination being connected in series with the B+ supply to the receiver circuits so that the total B current of the receiver flows through it. The field neutralizing control permits the current flowing through the field neutralizing coil to be varied from a maximum current of one polarity, through zero current, to a maximum current of the opposite polarity.

Conventional color picture tubes have aperture masks back of their face plates and supported by steel frames. I have found that with such a field neutralizing coil around and flush with the face plate of such a color picture tube, the high surge currents which occur when the receiver is turned on, cause the steel frame supporting the aperture mask to become magnetized in such a direction that its field decreases the strength of the field of the field neutralizing coil. A field neutralizing coil designed to give a shift in dot landing of the electron beam at the edges of a picture tube screen of .003", had the shift reduced to .001 because of the effect of the surge current on the steel frame.

This invention locates a field neutralizing coil in such a position on a color picture tube having an aperture mask supported by a steel frame, that the effects of surge currents on the steel frame are greatly reduced. In this position, there are components of the fields from the magnetized cathode ray tube shield and the aperture mask frame, which are perpendicular to the electron beam in both an upward and a cancelling downward direction. A field neutralizing coil located in this position and designed to give a shift in dot landing at the edges of a picture screen of .0035", had the shift reduced to only .003" by the effect of surge current. Thus, in one particular example the effect of surge current has been reduced by this invention to only 21% of the former value.

An object of this invention is to reduce the efifects of surge currents on the frame that supports an aperture mask of a color picture tube.

A further object of this invention is to locate the field neutralizing coil relative to the aperture mask frame so that deleterious magnetization of the aperture mask frame is minimized and the effectiveness of the field neutralizing coil is accordingly maximized. I

This invention will now be described with reference to the annexed drawings, of which:

FIG. 1 is a side view of a conventional color picture tube with a conventional field neutralizing coil located flush with the face plate of the tube as is conventional, a portion of the envelope of the tube being removed so 3,018,401 Patented Jan. 23, 1962 as to show portions of the aperture mask and its steel supporting frame, the field neutralizing coil being shown connected to a conventional field neutralizing control, and

FIG. 2 is a fragmentary view of a color picture tube with a field neutralizing coil embodying this invention, the fragmentary view of the picture tube corresponding to the removed envelope portion of the tube of FIG. 1.

In both FIGS. 1 and 2, the solid field lines with arrows are the field lines from the field neutralizing coil. In FIG. 1, the dashed lines with arrows are the field lines from the steel frame which supports the aperture mask. In FIG. 2, the dashed lines with arrows are the field lines from the aperture mask supporting frame, and from the shield around the tube.

Referring first to FIG. 1, an aperture mask type, color picture tube 10, has an aperture mask 11 supported by a steel frame 12. A magnetic shield 13 extends around a portion of the envelope of the tube. A field neutralizing coil 14 is mounted flush with face plate 15 of the tube. The coil 14 is connected to a pair of terminals 16 of a double-pole, double-throw switch 17, the blades 19 of which are connected across a potentiometer 20 which is connected in series with the B+ supply to the television receiver circuits with which the tube 10 is to be used. The switch 17 has another pair of terminals 18, reversely connected to the terminals 16. The B+ voltage source, together with the receiver circuits as indicated schematically by block 22, constitutes a constant current source connected across rheostat 20 and coil 14.

By placing the switch blades 19 in opposite positions to contact the terminals 16 or 18, currents of opposite polarities can be made to pass through the field neutralizing coil 14, and the current through the coil can be adjusted from maximum in one direction, through zero, to maximum in the other direction, by adjustments of the switch 17 and the potentiometer 20, to correct for axial components of the earths magnetic field. The construction and circuit of FIG. 1 are conventional.

High surge currents which appear when the receiver is turned on, cause magnetization of the mask 11 and frame 12 in a direction that decreases the field of the field neutralizing coil. The dashed lines with arrows which represent the field of the magnetized frame 12 are seen to be directioned opposite to the directions of the solid lines which represent the field of the coil 14. The field of the coil 14 is thus so weakened by the field of the frame 12 that such a coil designed to give a shift in dot landing at the edges of the screen of an associated color picture tube of .003", could only give a shift of .001".

This invention, instead of locating the field neutralizing coil flush with the face plate of a picture tube, locates such a coil 14 circumferentially around a magnetic shield 13, and spaced axially and rearwardly of the aperture mask frame 12, and around the converging portion of the envelope of the picture tube as shown by FIG. 2. With the field neutralizing coil so located, there are components of the fields from the magnetized shield 13 and from the magnetized frame 12 that are substantially perpendicular to the electron beam of the tube, in both an upward, aiding and a downward, cancelling direction, The dashed line 13A of FIG. 2 shows the aiding and cancelling components of the field of the shield 13 that are substantially perpendicular to the cathode ray beam, and the dashed lines 12A and 12B of FIG, 2 show the aiding and cancelling field components from the magnetized aperture mask frame 12 that are substantially perpendicular to the cathode beam,

A field neutralizing coil 14 located as shown by FIG. 2, and designed to give a shift in dot landing at the edges of the screen of an associated color picture tube of .0035, had the shift reduced to only .00 by the effect of surge current.

While the present invention has been shown in certain preferred embodiments only, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various changes and modificatons without departing from the spirit and scope thereof.

What is claimed, is:

1. In combination, a color television picture tube having a face plate, having an aperture mask back of said face plate, and having a frame of magnetizable metal supporting said mask, and means includinga field neutralizing coil around the envelope of said tube on the opposite side of said frame from said face plate, for neutralizing axial components of the earths magnetic field within said tube.

2. In combination with a color television picture tube having a face plate, having an aperture mask back of said face plate, having a frame of magnetizable metal supporting said mask, a magnetic shield around the envelope of said tube, and means including a field neutralizing coil disposed around said shield in a plane on the opposite side of said frame from said face plate, for neutralizing magnetic field components which extend perpendicularly to said aperture mask within said tube.

3. In combination, a color television picture tube having a face plate, having an aperture mask back of said face plate, having a frame of magnetizable metal supporting said mask, and having an envelope with a portion which decreases progressively in diameter back of said frame, and means including a field neutralizing coil disj, posed around said envelope portion and lying in a plane substantially parallel to and spaced axially from said aperture mask frame, for neutralizing axial components of the earths magnetic field within said tube.

4. In combination with a color television picture tube having a face plate, having an aperture mask back of said face plate, having a frame of magnetizable metal supporting said mask, and having an envelope with a portion which decreases progressively in diameter back of said frame; a magnetic shield around said envelope portion; and means including a field neutralizing coil around said shield and said envelope portion, for neutralizing axially extending magnetic field components Within said tube, said coil being disposed relative to said frame so that permanent magnetization of said frame by surge currents in said coil is of a polarity to aid the neutralizing effect of said coil.

References Cited in the file of this patent Sanford Mar. 24, 1959 Francken June 9, 1959 OTHER REFERENCES Law: A Three-Gun Shadow Mask Color Kinescope, Proceedings of the I.R.E., October 1951, pages 1193, 1194. 

